Cellulose processing in ionic liquid based solvents
Doctoral thesis, 2014
As the most abundant polymer in nature, cellulose has an undisputed role among the raw materials to be used in a sustainable future. From its native form, in wood or straw, cellulose can be processed into products such as paper and board. Through dissolution and precipitation, the range of cellulose based products can be increased to include textile fibers, thin continuous films, foams and membranes. Since cellulose is insoluble in most conventional solvents, ongoing research worldwide aims to find new, efficient and environmentally friendly solvent systems for biomass in general, and for cellulose in particular.
In this thesis, the solvent of focus was 1-ethyl-3-methylimidazolium acetate, commonly abbreviated as EMIMAc. It is an ionic liquid, and belongs to a class of solvents which was basically unexploited by cellulose chemists until just over a decade ago.
Results show that cellulose that is dissolved in EMIMAc, with or without a cosolvent, can be spun into continuous textile fibers using airgap spinning or wet spinning, or be cast into films. The properties of the produced fiber vary depending on the solution, cellulose sources and spinning parameters, such as drawing. For example, the regeneration medium was found to be of great importance for the crystallinity of regenerated films. Properties of regenerated cellulose can be further altered by drying conditions. It was also shown that some residual coagulation medium (water), which is time-consuming to remove in a solvent recycling step, can be tolerated in the EMIMAc to some extent if cellulose concentration or degree of polymerization is low. Finally, esterification of cellulose in EMIMAc was found to be improved by using cosolvents to regulate unintended acetylation, which until now, has been the dominant result in such reactions.